The traditional method of growing trees is in a tree nursery, which mainly comprises outdoor beds in which trees are grown for between 1 to 3 years, and sometimes longer. As required, the young trees are dug up in the late autumn, and sold as ‘bare-root’ stock. If properly protected in plastic sacks, bare-root stock can last for some weeks out of the ground before being planted out in their final positions. Species which resent root disturbance, which include holly and most conifers, are grown in containers. A nursery may include a polytunnel for propagation and early growth in trays or cells, and may grow a mixture of outdoor or ‘field grown’ plants, and others which are grown and sold in rootrainers, cells or pots.

Selecting and preparing a nursery site

In looking for a site, choose one which is easily accessible because frequent care is needed. A site which is secure from vandalism is also important. Private gardens, school or hospital grounds or other supervised sites are best. Allotments are also suitable. The site will be needed for a minimum of three years, so make sure you have sufficient tenure. As shown in the example below, a small nursery plot can produce a large number of trees.

Site selection

  • A suitable soil, which is workable in early spring, is vital. Heavy clay is difficult to work, but light sandy soils will dry out too quickly and are nutrient-poor. A light lime-free loam, of a good depth to retain moisture, is ideal.
  • A slight slope ensures good drainage, which is essential. Avoid steep slopes, as the soil will wash away. Also avoid an easterly slope, as the morning sun can cause damage after a heavy frost. On dewy mornings, the early sun can also scorch the leaves of young seedlings. The best choice is a slight slope to the west or north, or failing this, level ground. The site must not be in a frost hollow.
  • Shelter from the wind. Temporary screens of commercial windbreak material, hessian or similar may be needed. For the longer term, plant hedges for shelter.
  • A water supply is necessary.
  • See here for notes on maintaining soil fertility.

The following diagram is of a 3 x 4m tree nursery suitable for managing by voluntary groups. The aim is to produce young trees which are ready for planting out after 2 years in the nursery (1 + 1), with a small proportion being grown on for another year (1 + 1 +1). All the plants are transplanted each year, to encourage a good root:shoot ratio. This also allows annual incorporation of leaf mould or compost and thorough weeding of all the beds.

  • Sow sufficient seed to produce 4-500 seedlings per year.
  • Seedlings of most species should be 10-30cm high at the end of the first year, when they are transplanted or ‘lined out’.
  • Line out in transplant beds at spacing to suit species (Table 5c). At the end of the second year, there should be about 350 plants at least 20-40cm high (1+ 1), ready for planting in final positions.
  • Plants which are undersized or not required for planting out can be grown on for one more year (1 + 1 + 1).

Diagram of potential nursery layout

Fencing

The area must be protected against deer, rabbits and dogs. The seedbeds also need protecting against cats, birds and small animals. A fence which excludes rabbits and dogs can be made from 31mm gauge mesh, 1050mm high. The lower 15cm (6”) is buried under the surface as shown, to discourage burrowing. Preferably use coated rabbit-proof netting, such as ‘Sentinel Green’, which is galvanised and then treated with an anti-corrosive coating. With uncoated galvanised wire, the zinc used in the galvanising eventually makes the soil toxic.

Rabbit fencing

Beds and paths

Seedbeds must be made afresh each year. In commercial nurseries, tractors with special cultivators are used which create raised beds, normally 1.1m (43”) wide and about 10cm (4”) high, with the tractor wheels making the paths or alleys between, which are about 50cm (18”) wide. The soil in a raised bed is well drained and warms more quickly, promoting germination and growth. On sloping sites, run- off flows down the alleys, rather than washing through the beds. The beds are narrow enough to be hand-weeded from either side without treading on the beds. The sides of the beds tend to crumble during the season, so an 8cm (3”) strip is left unsown along the edges.

In small nurseries, raised beds can be made by digging out the soil from the paths and using it to raise the soil level in the bed. The sides of the beds can be retained with planks of wood, or left as a bank. Beds retained with planks can be topped up with loam or compost as necessary, rather than being remade each year. Raised beds are essential for seed sowing, but on well drained sites with a natural deep loam, are not essential for the other beds, called transplant beds.

On a small site, mown grass paths are best avoided, as the grass competes for available moisture. If using grass, make the paths wide enough to mow, and don’t have the young trees nearer than 15cm (6”) to the edge of the grass. Alternatively use paving, old carpet, sheet mulch material or similar to make temporary surfaces to stop the paths getting muddy. These materials can be lifted when the raised beds are remade.

Clearance and cultivation

On heavy soils which have not been cultivated for some time, it’s best to clear and dig in the autumn, to allow the winter frosts to break up the clods. light loams can be dug on a dry day in late winter or early spring, so clearance, cultivation and preparation of the beds can be done in one operation.

If the area is short grass, cut and remove the turves. Stack unwanted turves upside down in a nearby corner, where they will rot down to a fine loam, which is ideal for creating seedbeds. If the area is rough grass, mowing at intervals during the summer to convert to shorter grass will make removal of turves easier. For rough growth, dig over the entire area and remove all top growth and roots. All perennial roots must be removed from the beds. A small piece of couch grass or bindweed, for example, can wreck a seedbed. Alternatively a herbicide can be used, but cultivation will still be needed.

Dig the entire area to a spade’s depth. For heavy soils, fork over the bottom of each trench and leave the soil over the winter to weather. Mark out the beds, which are usually 1m (3’) wide so they can be planted and weeded without trampling on them. Dig soil evenly from the paths and throw it onto the beds, until the beds are 10-20cm (4-8”) higher than the paths. Use planks as desired to surround the beds, secured into the ground with steel pins or wooden stobs.

Level out the surface of the beds and then firm them down by treading them with a ‘shuffling’ walk. alternatively, use a thick plank and tread on it. The beds must be well consolidated before sowing to allow the soil moisture to reach the surface layers by capillary action, and prevent them from drying out in warm weather. A simple test is to press the bed firmly with the flattest part of a clenched fist. Consolidation is adequate when only a slight indentation can be made. Do not firm down the bed when the soil is too wet, or the soil structure will be damaged. The bed is now ready for sowing.

Sowing and growing on

As well as varying with species and strains, the size of seedlings at the end of the first growing season depends on various factors. The height depends on the sowing date, irrigation and whether they are grown under any form of covering. The stem diameter will increase with increased growing area, both above and below ground.

Sowing

Sowing is possible from early March to late April, depending on the area of the country, location and season. Delay the work if there is a cold, wet spell, and preferably sow on a dry, still day.

  • Large seeds should be sown singly. Space acorns and sweet chestnuts 5cm (2”) apart, and ash and beech 2.5cm (1”) apart. Using a dibber, make a hole twice the depth of the seed, sow, and then cover it with sieved soil or sand. Firmly compact to remove air pockets. Sow in rows to make it easier to spot the seedlings when they emerge. Protect with netting or fleece, and use traps as necessary against mice.
  • Acorns, beech and sweet chestnut can be sown in autumn. Temporary deep sowing is a traditional method for acorns, in order to protect them from mice and birds. Sow as described above, and then mark the top surface using a thin layer of sawdust, old plastic netting, strips of plastic sack or similar. Then cover this with an extra protective 10cm (4”) layer of soil. Then in early spring, rake off the top 10cm (4”) layer, and remove the plastic mesh or other marker.
  • Large and small seeds can be sown in drills. Using the back of a rake or the edge of a board, make a ‘valley’ or drill to the appropriate depth, and about 10cm (4”) apart. Sow the seed evenly along the drill, following the above spacings for large seed. Cover the drills with coarse sand or fine grit (see below).
  • Normally, small seeds are broadcast by hand, trying to get as even a coverage as possible. Table 5c gives the recommended sowing rates for different species. Carefully weigh seed into small amounts, say 25g for the lighter seeds, and sow over the appropriate measured area. With experience, this can be done by eye. Very light seeds such as birch and alder can be mixed with damp sand to try and get a more even coverage. Birch, being a tiny winged seed, should be carefully sprinkled from just above the surface of the soil, rather than being thrown.
  • After broadcast sowing, roll the bed with a garden roller to ensure good seed to soil contact.
  • Immediately after broadcast sowing, thinly cover with a layer of sand or grit. This prevents small seeds from blowing away, excludes light and keeps the seeds and soil surface moist. Use pale, coarse sand, or grit which passes through a 3-5mm sieve, and cover to a depth so the seed is just hidden. Spread using a sieve or riddle to give even coverage. Don’t use dark sand or grit, as this heats up in the sun and may damage the seedlings. Grit and sand must be lime free and silt free. Silt causes the grit to ‘cake’ or consolidate in rain. Fifty kg of grit covers about 4 square metres (92lbs covers 4 square yards). Don’t economise by using soil for covering small seeds, as sand or grit give much better results. Birch is usually left uncovered as it needs light to germinate, but the seedbed must be kept moist.

Protection

Seeds, seedlings and transplants need protection from birds, small mammals and cats. Birds and mice may take the seed before it germinates. Acorns, chestnuts and beech nuts are especially attractive to large birds such as rooks, wood pigeons and pheasants, and may also be eaten by mice and squirrels. Moles can disturb seedbeds and transplant beds, and cats are attracted to bare, finely cultivated soil. Grit on the surface discourages cats and mice. Voles can damage seedlings and young trees.

Immediately after sowing, stretch plastic garden netting with a mesh size of 20 x 20mm over the beds to protect them from birds and cats. Suitable netting is available from garden centres and other horticultural suppliers. A width of about 1.5m (5’) is suitable, and diamond-pattern netting which has some ‘stretch’ is easier to fit. raise the netting off the ground, on hoops of 8 or 10 gauge galvanised wire or 20mm plastic water pipe or similar. The netting must be pinned securely to the ground all around, at intervals of about 45cm (18”). Pegs, similar to tent pegs, can be made from lengths of galvanised wire, or are available from garden netting suppliers.

Protective netting

Remove  the  netting  once  the  first true  leaves  have developed.

Plastic netting is not proof against mice, voles or moles which can chew through or burrow underneath. Mice and voles are likely to be abundant where the seedbeds are close to hedges, long grass or other suitable habitat. lay spring or ‘humane’ traps at intervals around the beds, baited with chocolate. Use mole traps set in runs as necessary.

Extra protection may be needed for autumn-sown acorns, chestnuts and beech nuts, which are very attractive to mice. you may need to envelope the seedbed with panels of wire mesh (6mm gauge). Before you make the seedbed, lay a piece of mesh to give about 20cm (8”) soil coverage above. After sowing, cover the top with another piece of mesh and bend to close the sides. The top panel can be removed once the first true leaves have appeared. Sowing in protected pots or trays is another option.

Protecting autumn-sown acorns

As an alternative to netting, a ‘floating mulch’ or ‘fleece’ can be used, both as protection against birds, and to improve germination and growth rates. The fleece results in a higher soil and air temperature, higher relative humidity and soil moisture. Higher germination rates, faster growth and better one year seedlings are possible with most species, apart from beech, which is sensitive to higher temperatures. Fleece gives about 90% light transmission, allows natural ventilation and watering. It can be anchored by pegs, weights or by pinning to the surrounds of raised beds. Fleece is reusable if handled and stored carefully. Fleece should be removed once the seedlings start to lift it, as otherwise shoots can get entangled. For the first week or so after removal, replace at night or in cold or drying conditions, until the seedlings have hardened off.

Netting may be needed in addition for acorns and other large seed, as crows have been known to pierce the fleece in order to reach the seed.

Aftercare

Any weeds that appear in the seedbed are best removed by cutting through at just below ground level with a knife. If you pull them up, you may disturb the tree seeds and seedlings. Take great care not to mistake germinating trees for weeds. Weeding of newly germinating beds is best done by experienced workers.

Weeding must be done frequently, which means about every 2 weeks in spring and summer, and every month in the autumn and winter. Grass and other unwanted growth can appear at any time of year provided the weather is mild. Hoes can be used with care between rows of seedlings, but hand weeding is usually preferable.

Watering

Water the seedbeds whenever the soil begins to dry beneath the surface. Use a fine spray, preferably applied in the early evening. Avoid watering in bright sunlight, as the sun shining through the droplets can scorch the young leaves. Beds of birch or alder seed need to be kept moist throughout the germination and early seedling period.

Diseases and pests

There are several common diseases and insect pests which can cause damage to seedling trees. larger pests are dealt with above under ‘Protection’.

Damping off

This is caused by soil fungi, and can affect germinated seeds and young seedlings. Seedlings may fail to appear, or suddenly collapse. Damping off can occur in patches through the seedbed, or in pots or trays. Try and prevent it in polytunnels and greenhouses by good hygiene. This means cleaning benches, glass or polythene, cleaning pots after use, using clean soil-less composts and irrigating with clean water. Sow thinly, water sparingly and keep the tunnel well ventilated. Watering must be related to temperature, as excess moisture at low temperatures may cause the problem. As temperatures rise and growth increases, the volume of water applied can be increased. Established outbreaks cannot be controlled. As soon as you notice any signs of damping off, remove the affected seedlings and water the remainder with Cheshunt Compound.

Grey mould

Seedlings in greenhouses may be affected. Infected parts die back and give off a grey ‘smoke’ of spores when touched. Apply Captan immediately damage is seen, and then every 10 days until no mould is evident. Increase ventilation.

Mildew

This fungal disease can appear on two year old or older plants including oak, hawthorn and willow. It appears in warm dry weather, in April or May, when newly emerged leaves may be affected by spores produced from buds in which the fungus has overwintered. Pale brown spots appear on the undersides of leaves, from which a white mycelium spreads across the foliage. Avoid watering from above, but use capillary matting under pots or water outdoor beds with a seep hose. Diseased shoots should be cut off in the autumn to prevent the spores overwintering.

Chafers (Melolantha spp) and cutworms

The grubs of chafers feed on the roots of seedlings and transplants. Cutworms, which are the caterpillars of various moth species, gnaw at the root collars of seedlings, usually cutting them off at soil level. Apart from using insecticides, control of both pests can usually be achieved by regularly cultivating the soil and removing the grubs or caterpillars by hand.

Ants

Ants may sometimes cause problems in seed and transplant beds by taking seed, building nests and loosening the soil so that plants wilt and die. Use ant killer on the nests and runs. Some gardeners plant lavender as a deterrent to ants.

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